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%I #15 Feb 24 2018 10:11:00
%S 4,4,20,246,150610,28628772458,4633718454684972107216,
%T 32270052939985266099596531363945117655631355,
%U 1531822012919710742180024988940181184501391371231597927081244972822399811859680584475111
%N Denominators of r-Egyptian fraction expansion for 1/Pi, where r = (1, 1/4, 1/9, 1/16, ...).
%C Suppose that r is a sequence of rational numbers r(k) <= 1 for k >= 1, and that x is an irrational number in (0,1). Let f(0) = x, n(k) = floor(r(k)/f(k-1)), and f(k) = f(k-1) - r(k)/n(k). Then x = r(1)/n(1) + r(2)/n(2) + r(3)/n(3) + ..., the r-Egyptian fraction for x.
%C See A269993 for a guide to related sequences.
%H Clark Kimberling, <a href="/A270376/b270376.txt">Table of n, a(n) for n = 1..12</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/EgyptianFraction.html">Egyptian Fraction</a>
%H <a href="/index/Ed#Egypt">Index entries for sequences related to Egyptian fractions</a>
%e 1/Pi = 1/4 + 1/(4*4) + 1/(9*20) + 1/(16*246) + ...
%t r[k_] := 1/k^2; f[x_, 0] = x; z = 10;
%t n[x_, k_] := n[x, k] = Ceiling[r[k]/f[x, k - 1]]
%t f[x_, k_] := f[x, k] = f[x, k - 1] - r[k]/n[x, k]
%t x = 1/Pi; Table[n[x, k], {k, 1, z}]
%o (PARI) r(k) = 1/k^2;
%o f(k,x) = if (k==0, x, f(k-1, x) - r(k)/a(k, x););
%o a(k, x=1/Pi) = ceil(r(k)/f(k-1, x)); \\ _Michel Marcus_, Mar 21 2016
%Y Cf. A269993.
%K nonn,frac,easy
%O 1,1
%A _Clark Kimberling_, Mar 20 2016
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